Traditional Japanese houses are not insulated. They are built to allow air to flow through them which ventilates and helps to prevent mould, allows smoke to rise into the thatch, and all of that. The focus of traditional buildings is managing summer heat and humidity, not the hypothermic chill of winter.
However, most people in Japan don’t live in old farmhouses; they live in uninsulated modern construction. Rooms are cold and drafty because that’s how houses have always been and why change tradition?
Though the JIS standard since the mid 90s has been for “pair glass” (double paned) windows, and a certain thickness of insulation in outer walls and roof, it’s still a mark of excellence to have them. People often ask if we are putting pair glass in the new house. Hell, yes.
Since cold and drafty is not my thing, 555 is up to spec with the mid-90s. We have pair glass! There is “glasswool” insulation for the walls & roof. Insulation under the floor! We will have a six-sided envelope of similar rated insulation systems.
We could have leaped forward into this century’s standards and sprung for triple-pane windows and thicker insulation. But it will be such an improvement to have moderate insulation that I will happily stick to the 90s standards for half the cost.
Adding the insulation creates yet another turning point in the way the house feels. The charming filtered light from the Tyvek sheets is gone. The walls feel more solid now. It is cosy and a little darker inside. I like it very much.